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AY BMSc Implant Technology > Unit 6d: Surgical Fracture Fixation > Flashcards

Unit 6d: Surgical Fracture Fixation Flashcards

(96 cards)

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1
Q

What are the 3 types of internal fixation?

A

Bone screws
Bone screws and plates
Intramedullary nails

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2
Q

What is the mot commonly used material for fracture fixation?

A

Stainless steel

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3
Q

What are the advantages of using titanium over stainless steel in fracture fixation?

A

Strong
Inexpensive
Biologically more inert than stainless steel
Less likely to cause allergies

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4
Q

Why must plates and screws be made of the same material?

A

Otherwise galvanic corrosion of the implants is likely to occur

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5
Q

What is a screw?

A

A mechanism that produces linear motion as it is rotated

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6
Q

What 2 factors are needed for a screw to be able to fix together 2 objects (Block 1 and Block two)?

A

Head of the screw is wider than the diameter of the shaft so it pushes the 2 objects together

The thread does grip Block 1

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7
Q

How can it be ensured that the thread does not grip Block 1?

A

The screw must have no thread on the section nearest to the head where it touches Block 1
or
Block 1 must have a pre-drilled hole in it which is larger than the screw thread

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8
Q

What would happen if the thread gripped both blocks?

A

The screw would move through both blocks so that it could not compress them together - no matter how close they were

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9
Q

What is the holding together strength of the 2 object dependent on when screwed together?

A

Strength of the screw material
Strength of the object material
Design of the screw thread

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10
Q

What are the 2 functions of the head of a screw?

A

Provide a butteress to stop the whole screw sinking into the bone

Provides a connection with the screwdriver

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11
Q

When would a larger buttress on a screw be used/

A

In soft bone

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12
Q

What is the most common drive connection shape in bone screws?

A

Hexagonal

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13
Q

Why do bone screws commonly use a hexagonal shaped drive connection?

A

Gives an effective coupling unlikely to be damaged in the screwing process

The very positive interlock between screwdriver and screw makes it easy to use - no axial force required to retain the driver in the head

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14
Q

Other then hexagonal what other shape drive connection is also very effective and now used in many commerical bone screw systems?

A

Star shaped

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15
Q

What is the most common undersurface shape in standard bone screws and why?

A

Rounded

Max area of contact between screw head and bone after countersinking - reducing the risk of a zone of excessive stress

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16
Q

Why is careful screw design important?

A

To avoid stress raisers

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17
Q

What are the 3 diameters to be considered in a screw?

A

Core diameter
Shaft diameter
Thread diameter

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18
Q

What is the core diameter of a screw?

A

The smallest diameter of the threaded section of the shaft

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19
Q

Which diameter determines the strength of a screw?

A

The smallest diameter (can be core or shaft diameter) - greater the smallest diameter the stronger the screw

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20
Q

What are the 3 important aspects of the thread?

A

Shape
Depth
Pitch

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21
Q

Why are most bone screws flat on the upper surface (in contact with the bone) and rounded underneath?

A

So they provide a wide surface on the pulling side and little frictional resistance on the underside (more torque goes into pulling the objects together and is less wasted on simply overcoming friction during insertion of the screw

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22
Q

Why is a deeper thread more desirable in cancellous bone?

A

As it will capture more material between the threads and so increase the resistance of the screw to pulling out

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23
Q

What is the pitch of a screw?

A

The linear distance travelled by the screw for a complete (360) turn of the screw

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24
Q

What is tapping?

A

The process of cutting a thread

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25
What is a self-tapping screw?
A screw which has a cutting tip that enables it to cut its own "female" thread track as it is being inserted
26
What type of screws are used in cancellous bone?
Self-tapping screws
27
What is meant when it is said that the malleolar screws is self-drilling?
It can drill a hole in the cancellous bone without the need to use a separate drill bit
28
Why is is not possible for a screw to "force" a thread track in cortical bone?
Too much torque would be required
29
What shape is the tip of cancellous bone screws?
Corkscrew
30
What are the benefits of "pre-tapping"?
Screw is easier to insert Most of the torque applied on tightening is converted into compression No bone fragments jamming between the screw and thread
31
What are flutes in tapping instruments have them?
Channels which provide a route for cuttings to escape
32
Why do cortical screws not have flutes?
Because bone can grow in to the flute and so make removal difficult
33
What is lagging?
The process of compressing 2 objects together
34
What are the 2 ways in which screws can achieve the lag effect?
Can be designed specifically as lag screws Can be inserted in such a way that any screw may act as a lag screw
35
What to lag screws look like?
They are partially threaded only at the section nearest the tip
36
How can any screw be made to act as a lag screw?
By drilling a hole slightly larger than the screw thread diameter in the cortical bone fragment
37
What are 5 applications of screws in fracture fixation?
Prevent sideways displacement of fragments Hold a plate against bone Increase the grip of an intramedullary nail on the bone Permit displacement in an axial direction As part of an external fixator assembly
38
What fractures are screws and plates indicated for?
Forearm fractures Around joints where complete reconstruction of the cancellous bone is not possible
39
What might cause a fracture where complete reconstruction of the cancellous bone is not possible?
Particularly violent fractures Soft bone found after a delay of a few days between injury and surgery If the bone is unnaturally soft (e.g. old age)
40
What is osteosynthesis?
Reconstruction of a fractured bone by surgical and mechanical means
41
What is "bridging technique"?
When 2 main bony shaft fragments are linked by means of a plate to restore bone length and alignment (small fragments are left unfixed but their blood supply is left undisturbed)
42
How does the wall thickness of a bone affect it's strength?
Thin walled bones are weaker then thick-walled bones
43
What is the aim of plate fixation?
To achieve load sharing between plate and bone until the healing bone is strong enough to take the load efficiently
44
What usually causes bending and subsequent failure of a plate?
If the fractured bone has not been accurately reassembled
45
What is stress reversal?
When a plate in bent back and forwards when the incomplete bone-plate construct is loaded
46
What is the result of stress reversal?
Early fatigue failure of the plate
47
What can be done to minimise fatigue failure of a plate?
Plates and screws should form as stable a construct as possible Limit damage to the bones blood supply Plate should be placed in a position relative to the broken bone so that it is minimally stressed Position plate so uninjured tissues are ot unduly damaged Make plate from as strong as possible material which can tolerate stress reversals
48
In what 3 situations are plates indicated?
When anatomical allignment must be restored accurately Where the use of screws is inadequate When load sharing may be achieved with confidence
49
Why might the use of screws alone in fracture fixation be inadequate?
Because large bending forces distort fractures fixed only by screws
50
If load sharing can't be achieved with confidence but plates are still indicated what can be done?
Bone graft may be added at the site of any deficit - will accelerate the healing of the bone before the plate becomes at risk from fatigue failure)
51
What areas of the body are plates commonly used in?
Around joints Forearm Pelvis (especially around the acetabulum) Face and jaw
52
Why are plates used around joints in particular?
Anatomical restoration is very important - failure can lead to OD
53
What is eccentric loading?
When bones are NOT loaded evenly along their axes
54
What does eccentric loading cause?
Loaded bone to distort more on one side than the other
55
How can plates be used in eccentric loading?
Fix the plate on the side tending to open (the tension side) to counteract the eccentric load
56
Why might it not be possible to place a plate on tension side of a fracture?
Need to respect the blood supply of the boy fragments Risk of tethering mobile structures (e.g. tendons)
57
How can compression of the bone on the opposite side of the attachment of the plate be encouraged?
Bend the plate slightly | aids the load sharing between plate and bone and adds to stability
58
What is the disadvantage of all plating techniques?
Need for a lot of soft tissue stripping - further damages blood supply to already damaged area - will contribute to delay in healing and add to risk of developing an infection
59
What are pins also known as?
K wires
60
When are pins most commonly used?
Small bones (occasionally in upper limb long bones in small children)
61
Why might pins be used in conjunction with flexible wire?
To achieve compression between 2 small bone surfaces (e.g. patella fracture)
62
What is cerclage?
The use of a ring or loop to bind together the ends of an obliquely fractures bone
63
What are the 2 uses of flexible wire?
Statically - by encircling or crossing the fragments Dynamically - as a tension band
64
Why have nails replaced cerclage in most situation?
Nails do less damage to the blood supply and if used properly are much more robust
65
When is cerclage of cracked bones particularly useful?
In fragments of bone around endoprostheses (e.g. during revision hip surgery)
66
How is flexible wire used in the management of tibia fractures?
As a tension band - uses the power of surrounding muscle to produce compression at the fracture site
67
Why has wire fallen out of routine use?
It's awkwardness in use and need to twist it properly (over-twisting causes breakages) - surgeons find some of the newer techniques re more elegant in execution
68
What is the function of an intramedullary nail?
As a form of internal splint which stabilises long bone fractures with minimal damage to the surrounding soft tissues
69
What is the anterograde technique of intramedullary nailing?
Nail is inserted into the bone from one end whilst not disturbing the fracture site - x-ray image intensifier is needed
70
What is the retrograde technique of intramedullary nailing?
Fracture site opened by soft tissue dissection and the fracture end delivered into the wound for reaming and insertion of the nail
71
What is the difference between the reamed and unreamed technique of nailing?
Reaming = Paring off the inner surface of the bone Unreamed = use solid thinner nails so that they may be inserted without damage to the inner blood supply of bones
72
What are the 3 most important factors to consider in nail design?
Material of which it is made How much of the nail is in contact with the bone for any particular fracture The dimensions and shape of the nail
73
What material are most nails made of?
Stainless steel
74
Why is titanium generally not used for nails?
More susceptible to weakening either if a hole is drilled aross it or if it is accidentally abraded during insertion or locking
75
What is notch sensitivity?
When a nail is accidentally abraded during insertion or locking
76
What is the working length of a nail?
The length of a nail that transmits load from one main fragment of a fractured bone to the other
77
Which is stronger, a solid or hollow nail of the same diameter?
Solid nail
78
How can the stiffness of a hollow nail be altered?
Making the walls thicker or thinner (thicker = stronger and stiffer)
79
What is the advantage of a somewhat flexible nail?
Has a little "give" on insertion which makes it easier to put in and allows the nail to deform slightly to conform to the natural shape of the bone
80
What is the disadvntage of very stiff nails?
May damage the bone if there is any discrepancy between the shape of the nail and that of the bone
81
What effect does a longitudinal slot have on the mechanical properties of a nail?
Makes it much more flexible But loses some overall bending and especially torsional strength
82
Give examples of the ideal indications for nailing
Transverse and short oblique fractures of the femoral and tibial shifts Comminuted fractures of tibia and femur (provided cross locking capabilities are available) Pathological shaft fractures (especially in osteoporotic bone) Delayed or non-union of the shafts of the femur or tibia Selected open fractures
83
What extra equipment is needed to place nails and why?
X-ray image intensifier - so nail can be sited accurately in the medullary canal of the broken bone
84
Name 2 contraindications to nailing
Children (nail may damage growth plates) When there is a fracture involving an adjacent joint
85
What are the 3 configurations nails can be used in?
Simple nial with no additions With screws With plates
86
When in particular are nails used in association with plates?
To treat fractures of the proximal and distal femur
87
What are the advantages of using a nail alone?
Maintains a fairly accurate anatomical alignment Permits early weight bearing
88
Which bones are nails most commonly used on their own?
Femur Tibia Humerus
89
How can the effective working length of a nail be increased?
By adding cross screws
90
What effect does the addition of cross screws have on nailing?
Ensures good rotatory control (independent of the contact between nail and bone Increases the length of long bones which can be nailed
91
Why is the femur being constantly bent when under load?
135 degree offse of the femoral neck - creates an angle of about 7 degrees between the axis of the femur and the tibia when the tibial plateau is orientated horizontally, parallel with the ground
92
Which group are fractures of the femoral neck most common in?
Old age (particularly women who suffer from osteoporosis)
93
What position does the femur naturally sit in after an extracapsular fracture?
Proximal fragment keels over medially and for the femur to shorten
94
What is the degree of displacement of a femoral fracture dependent on?
Degree of damage to the medial part of the upper femoral shaft
95
How are femoral neck fractures plated?
On the lateral side
96
What are the complications of nailing?
Reamers (used to widen cavity) can get stuck or penetrate through to the outside of the bone Nail inserted in the wrong orientation (rotatory misalignment is common) Infection

AY BMSc Implant Technology (13 decks)

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